1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing semiconductor devices, particularly metal insulator semiconductor (MIS) devices, which can improve the performance of the devices, and more particularly to a method and apparatus for manufacturing semiconductor devices which can reduce interface states at the interface between an insulating film and the semiconductor substrate of the device.
2. Description of the Related Art
In semiconductor devices, particularly metal insulator semiconductor (MIS) devices, the energy levels within the band-gap existing at the interface between the insulating film and the semiconductor substrate of the device; i.e., so-called interface states, adversely affect the electrical characteristics of the MIS devices. Therefore, there has been a great demand for reduction of the density of the interface states.
Among MIS devices, MOS (metal oxide semiconductor) devices are in most common use. In the MOS devices, the interface states existing at the interface between the insulating film and the semiconductor substrate cause a decrease in the mobility of carriers, instability in the flat band voltage, a decrease in reliability in relation to breakdown of the oxide film, and an increase in a leak current density. Among these problems, an increase in the leak current density is a significant problem to be solved.
Conventionally, a reduction in the density of the interface states has been performed through use of a method in which an oxide film is formed on a semiconductor substrate, which is then heated in a hydrogen atmosphere or in an atmosphere of an inert gas such as nitrogen or argon (see, for example, B. E. Deal, Journal of Electrochemical Society, Vol. 144, p. 226, 1967). It is considered that when a semiconductor substrate having an oxide film is subjected to heat treatment in a hydrogen atmosphere, hydrogen atoms terminate dangling bonds at the surface of the semiconductor resulting in the deactivation of the dangling bonds, so that the density of the interface states can be reduced.
However, in the conventional method, the semiconductor substrate must be heated to a temperature as high as 400-1200.degree. C. when the heat treatment is performed in a hydrogen atmosphere and to a temperature as high as 900-1200.degree. C. when the heat treatment is performed in a nitrogen or argon atmosphere. Also, when the heat treatment is performed in a hydrogen atmosphere, the bonding force between the semiconductor substrate and hydrogen atoms is not strong, and therefore the dangling bonds can be easily terminated at a temperature as low as 400.degree. C. However, the hydrogen atoms bonded to the semiconductor substrate through heat treatment are easily released when the semiconductor substrate is heated to a temperature higher than that used during the heat treatment, and the effect disappears. Therefore, a limitation is imposed on the temperatures used in heat treatment processes subsequent to the hydrogen process.
Meanwhile, a high temperature annealing process in an inert gas such as nitrogen or argon has been used. However, the purpose of this high temperature annealing is not to terminate dangling bonds of a semiconductor with nitrogen atoms or argon atoms, but to align the crystals of the semiconductor. Therefore, heat treatment must be performed at a temperature of 900.degree. C. or more. However, heat treatment performed at a temperature of 900.degree. C. or more is not suitable for micro-devices, which must be subjected to heat treatment of a lower temperature; otherwise the depth of diffusion becomes too large.